A flush joint tubular connection has inner and outer diameters substantially the same as the tubing joints which the connection connects.
A flush joint tubular connection made by the Hydril Co., and covered by numerous patents comprise a first straight thread, a second straight thread of sufficient diameter to pass within the bore of the first thread and a tapered mating seal between the two joints of tubing which is a premium joint of high cost and according to published data, enjoys only 42% axial strength with regard to the pipe wall.
Standard A.P.I. non-upset tubing connections comprise couplings having outer diameters considerably larger than the pipe outer diameter but still only enjoy approximately 42% efficiency as above. A.P.I. does list a "turned down" collar outer diameter to increase clearance between strings, however, the "turned down" diameter still exceeds substantially, the pipe outer diameter.
No prior art discloses a tubular connection having tapered threads, that when properly assembled, effects optimum stresses within the small end of the external thread and within the large end of the internal thread so as to provide a connection of maximum efficiency. Conventional pipe connections have threads with like tapers and result in a constant diametrical interference along the taper between the external and internal threads, thereby causing excessive stresses Excessive stresses reduce the joint strength and an increased wall thickness rules out a flush joint connection.
It is therefore clear that a connection having a high efficiency as provided by the instant invention is needed for use within oilwells and other pipe assemblies wherein radial clearance is limited.